 Over 60% of our body is made up of water. While food can supply some of the water we need, it's easiest and most common for us to drink the water we need. Most women need 2.7 liters a day, and most men need 3.7 liters a day. Don't want to measure or count ounces? Just look at the color of your urine. Pale yellow indicates adequate hydration. With your body, I'm ABC's Dr. Jennifer Ashton.